Pre-Production
WM8904
ANALOGUE-TO-DIGITAL CONVERTER (ADC)
The WM8904 uses stereo 24-bit, 128x oversampled sigma-delta ADCs. The use of multi-bit feedback
and high oversampling rates reduces the effects of jitter and high frequency noise. An oversample
rate of 64x can also be supported - see “Clocking and Sample Rates” for details. The ADC full scale
input level is proportional to AVDD - see “Electrical Characteristics”. Any input signal greater than full
scale may overload the ADC and cause distortion.
The ADCs are enabled by the ADCL_ENA and ADCR_ENA register bits.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R18 (12h)
Left ADC Enable
1
ADCL_ENA
0
Power
Management (6)
0 = ADC disabled
1 = ADC enabled
Right ADC Enable
0 = ADC disabled
1 = ADC enabled
0
ADCR_ENA
0
Table 9 ADC Enable Control
ADC DIGITAL VOLUME CONTROL
The output of the ADCs can be digitally amplified or attenuated over a range from -71.625dB to
+17.625dB in 0.375dB steps. The volume of each channel can be controlled separately. The gain for
a given eight-bit code is detailed in Table 11.
The ADC_VU bit controls the loading of digital volume control data. When ADC_VU is set to 0, the
ADCL_VOL or ADCR_VOL control data will be loaded into the respective control register, but will not
actually change the digital gain setting. Both left and right gain settings are updated when a 1 is
written to ADC_VU. This makes it possible to update the gain of both channels simultaneously.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R36 (24h)
ADC Volume Update
8
ADC_VU
0
ADC Digital
Volume Left
Writing a 1 to this bit will cause left
and right ADC volume to be updated
simultaneously
Left ADC Digital Volume
00h = Mute
7:0
ADCL_VOL
[7:0]
1100_0000
(0dB)
01h = -71.625dB
02h = -71.250dB
… (0.375dB steps)
C0h = 0dB
… (0.375dB steps)
EFh to FFh = +17.625dB
(See Table 11 for volume range)
ADC Volume Update
R37 (25h)
8
ADC_VU
0
ADC Digital
Volume Right
Writing a 1 to this bit will cause left
and right ADC volume to be updated
simultaneously
Right ADC Digital Volume
00h = Mute
7:0
ADCR_VOL
[7:0]
1100_0000
(0dB)
01h = -71.625dB
02h = -71.250dB
… (0.375dB steps)
C0h = 0dB
… (0.375dB steps)
EFh to FFh = +17.625dB
(See Table 11 for volume range)
Table 10 ADC Digital Volume Control
PP, Rev 3.3, September 2012
49
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
